The present invention generally relates to a structural testing facility and, more particularly, to a testing facility for aircraft fuselage panels under various loading conditions.
During the past few decades, aircraft safety has been an important issue to design and maintenance engineers. Aircraft fuselage panels are subject to various types of loadings during normal operations and can develop cracks or failures by the process of fatigue. Such cracks grow slowly with increasing time and service, finally reaching a critical length of crack that can cause rapid propagation and catastrophic failure of an aircraft.
To understand and assess the effects of crack growth and residual strength of fuselage structures, several facilities have been developed to apply fight load conditions to large or full-scale models. For example, Rouse et al., AIAA paper No. 1423, 2003, discloses the Combined Loads Test (COLTS) facility at NASA Langley Research Center. In the COLTS facility, axial tension/compression combined with body torsion can be applied through moveable end platens to a curved stiffened fuselage panel. Also, internal pressurization develops partial hoop loading to simulate the cabin pressure. The segmented pressure box allows for torsional/axial displacement. However, the COLTS facility has the following characteristics: 1) an extensive FEM modeling is required to determine proper shear reaction, 2) it is difficult to develop full hoop loading in combination with torsion loading, and 3) the facility requires complex control algorithms.
Bakuckas, DOT/FAA/AR-01/46, discloses the Full-Scale Aircraft Structural Test Evaluation and Research (FASTER) facility at FAA William J. Hughes Technical Center. Using the FASTER facility, curved panels that are similar to a typical narrow-body fuselage structure consisting of skin, frames, shear clips, stringers, and either longitudinal splices or circumferential butt joints can be tested under biaxial tension loading. Also, discrete water actuated load systems are combined with internal air pressurization to develop full hoop loading. Shear stress can be applied to the periphery of a test panel via a cam actuated shear box. However, the FASTER facility fails to apply compression loading to the panel and the success of shear box performance may be questionable.
At http://www.ima-dresden.de/englisch/starteng.htm, the Curved Panel Test Fixture of IMA Gmhb Dresden has been disclosed. This facility can apply biaxial tensile loading to a curved panel via actuated load systems with internal air pressurization. However, it is not known whether the facility has the capability to load shear, compression loading or any combination thereof. A further example for panel testing facility can be found at Foster-Miller test Laboratory, Waltham, Mass. The D-Box test fixture of the Foster-Miller test laboratory can be used to test fuselage panels under biaxial tensile loading via actuated load systems with internal water pressurization. However, no attempt to apply full body loading has been made in that facility and test results are questionable.
D-Box test fixture for 777 Fuselage Development at Boeing Structures Test Laboratory, Seattle, Wash., is used to test fuselage panels under biaxial tensile loading due to internal air pressurization only. In that facility, the periphery of a test panel is rigidly attached to a pressure box. Also, this facility may need further development to accommodate the simulation of full body loadings. The Pie Fixture Test Facility at Northrop Grumman Structural Laboratory can test a fuselage panel under axial tension/compression combined with body torsion applied through moveable end platens. However, the facility has no internal pressurization mechanism, and therefore, cannot develop hoop loading. Also, it does not have any structure to develop proper shear reaction on the test panel.
A further example of panel testing facility is disclosed by Fields et al. at http://www.dfrc.nasa.gov/DTRS/2004/PDF/H-2488.pdf. As disclosed by Fields et al., the “Combined Loads Test Fixture for Thermal-Structural Testing Aerospace Vehicle Concepts” at Dryden Flight Research Center can test a uni-axial loaded flat panel with shear introduced through a “picture” frame. The panel may be subject to thermal conditioning from room temperature to 915° F. However, the facility cannot apply pressure or hoop loads as the test panels are flat. A still further example for panel testing facility is the Cryogenic Pressure Box Test facility at NASA Langley Research Center, as disclosed by Glass et al. at http://techreports.larc.nasa.gov/ltrs/PDF/2003/aiaa/NASA-aiaa-2003-1423.pdf. The Cryogenic Pressure Box can test a bi-axial loaded curved panel under cryogenic conditioning. However, this facility has not been known to test the panel under controlled pressure, hoop, or shear loading.
As is well known, aircraft fuselage panels are subject to one or more loads during normal operation, where the loads may include hoop load due to internal cabin pressure, longitudinal load (or, equivalently, axial tension/compression load), torsion and shear loads. As existing panel facilities can partially simulate these loads, there is a need for a facility that has a capability to simulate these loadings, either individually or in combination thereof, and that can test curved fuselage panels under more realistic flight loading conditions.